Preparation of SiC_w/Yb₂Si₂O₇ composite powders for environmental barrier coatings

In order to prolong the lifetime of environmental barrier coatings (EBCs) produced by thermal spraying, Yb₂Si₂O₇ powders doped with SiC whisker(SiC_w/Yb₂Si₂O₇) as feed stocks was prepared by ball milling, spray drying and vacuum sintering. The morphology, phase composition, particle size, flowability and densification of the powder were analyzed by TG-DSC, XRD, SEM and other methods. The SiC whisker was wrapped into the nanometer agglomerated powder by spray drying. The particle size varied by different spray drying parameters. Powders used for atmospheric plasma spraying were prepared by spray drying, optimal particle size can be obtained under 250 °C inlet temperature, 0.05 MPa atomization pressure, and a peristaltic pump rate of 60 r/min. With the increase of vacuum calcination temperature, the density and flowability of powders are improved, and the composition of the powder changed from Yb₂O₃ to Yb₂SiO₅ and finally to Yb₂Si₂O₇. The optimal compactness and flowability of the powders were obtained at the sintering temperature of 1300 °C with minimal surface porosity. SiC whisker was not oxidized during the vacuum sintering and still maintained the original whisker morphology. The densification process of recombinant particles and its mechanism were analyzed in terms of surface morphology and cross section.